The use of a single resistance wire formed into a helical coil for use in electric resistance heating either for heating moving air, for radiant heating, or for convection heating is well known in the prior art. In one type of heater, the resistance coils are energized to heat air passing over the coils, the heated air then being directed in a particular manner for heating purposes. One application using such a heater is an electric clothes dryer.
Examples of open coil heaters are found in U.S. Pat. Nos. 5,329,098, 5,895,597, 5,925,273, 7,075,043, and 7,154,072, all owned by Tutco, Inc. of Cookeville, Tenn. Each of these patents is incorporated by reference in its entirety herein. One type of an open coil electric resistance heater is a two stage heater described in U.S. Pat. No. 7,075,043. A side view of this type of heater is shown in FIG. 1 and designated by the reference numeral 10. The heater 10 has two heater elements 10a and 10b, optimally for use in a clothes dryer. The elements 10a and 10b are supplied with electricity via terminals 12 extending from the terminal block 28. The heater elements 10a, 10b are supported by a support plate 14, which in turn supports a plurality of support insulators 16, typically made of ceramic material and which are well known in the art. The support insulators 16 support and isolate coiled portions of the elements, 10a and 10b, during operation of the heater.
The heater 10 includes opposing sidewalls (one shown as 6 in FIG. 1), wherein projections in the plate 14 extend through slots 20 in the sidewall 6 to allow the sidewalls to support the plate.
Each of the electric heater elements, 10a and 10b, is arranged in series of electrically continuous coils which are mounted on the plate 14 in a spaced-apart substantially parallel arrangement. Each heater assembly 10a and 10b is arranged substantially equally and oppositely on both sides of the plate. Crossover portions 22a and 22b of each heater element 10a and 10b are provided wherein each crossover links one coil of each of the elements mounted on one side of the plate 14 with another coil of the same element found on the other side of the plate.
Electricity is supplied to the heater assembly through the terminal block 28. The heater elements, 10a and 10b, are arranged so that the terminal connector portions or wire leads 32 and 34 which extend from an end 38 of each of the mounted coil sections to the terminal block are as short as possible. This aids in eliminating or reducing the need for supporting the connector portions. For the longer runs, the wire leads, 32 and 34, are partially enclosed with an insulating member 36. The insulating member 36 may be formed from any type of insulating material suitable for this purpose, e.g., a ceramic type. The insulating member is generally tubular in shape and rigid.
Another type of heater manufactured by Tutco, described in U.S. Pat. No. 7,947,932 (herein incorporated by reference) is an improvement over the heater shown in FIG. 1, in that the heater coils are parallel to air flow to minimize noise, prevent coil shadowing, and promote heat transfer from the heater coils to the air stream.
In the manufacture of appliances and equipment, especially clothes dryer manufacture, that require open coil electric heaters mounted in an air duct to heat air flowing through the duct, there is a constant need to provide an inexpensive method of making an electric heater having multiple stages of heat such that each stage provides some heat to each side of a support plate. In the prior art of open coil heaters having heater coils supported by ceramic insulators held in metal plates, one method of providing two stages of heat is to have one heater coil completely assembled on one side of the plate and the second coil on the opposite side, see U.S. Pat. No. 7,154,072. Upon energizing the first stage of heat, only the air on one side of the plate is heated making for a less than desirable heat distribution for the first heating stage.
Another method to improve heat distribution is to route the first stage coil so a portion of the heater coil is on one side of the support plate with the remainder of the coil routed on the opposite side, see U.S. Pat. No. 7,075,043 as one example. When these types of heaters are energized, heat is supplied to both sides of the duct during first stage heating. The second heat stage coils are similarly assembled to complement the first stage. This is an expensive design, as the ends of the heating element wire must be covered with special designed ceramic tubes or ceramic beads for electrical isolation to prevent grounding or reduction of electrical clearance, see the insulating members 36 in FIG. 1 as an example. Some designs use special designed ceramics to secure the heating element wire ends to prevent shorting, grounding, or the reduction in electrical clearance as the wires are routed to terminals. A well accepted method long used is to provide individual termination points located immediately adjacent to the element coil ends. This is an expensive alternative, as power connections must be routed to multiple locations. Also, it is often impractical as some terminal locations may require power connections be made in excessively hot areas resulting in rapid deterioration under heat. Therefore, there is a need in the industry for a two stage, open coil electric heater that is inexpensive and has an arrangement wherein the first stage of the heater heats both sides of the air duct with the second heating stage complementing the first.
In the prior art there are usually either threaded style bolts or studs or blade or quick connect termination for power connection. Crimp style terminals made of flat metal stock for blade or quick connect termination crimped around resistance ends is well known and is presently sold by the TYCO Corporation. In the prior art, it is a common practice when bolt and threaded stud terminal style terminals are required for power connection, that these terminals are attached to element wire ends by welding, crimping, or pressure connection.
Welding is usually done by first mechanically staking the element wire ends into a slot in the head of a terminal bolt and then welding the two together. Crimping heating element wire ends to threaded bolts is accomplished by creating a tube style opening in one end of threaded stud terminals, inserting the heating element wire ends into the tube openings, and then mechanically closing the tubes so as to create a crimp connection. The least desirable connections are pressure connections in which resistance wire coil ends are looped around terminal bolts or threaded studs, then “sandwiched” between a combination of washers and nuts, whereby subsequent tightening of the nuts create electrical connections.
In the prior art, heating elements made as above are routed and assembled into the intended positions with heavy termination bolts attached to the coil ends. When a common threaded terminal power connection is needed, as for two stage or other multiple stage heaters, common element wire ends share a common terminal bolt or stud. When this type of connection is needed, the various methods of connection described above are followed except two or more element wire ends are connected to the required common terminal. For the welded connection, two or more common element wire ends are placed in the terminal bolt slot, mechanically staked then welded as above. For the crimp method, two or more common element wire ends are placed into the tube opening and crimped as above. For the pressure connection method, two or more common element wire ends are looped together then “sandwiched” as above and the termination completed. Thus, for the three prior art termination methods above, at least one end each of heater wire elements of multiple stage heaters share at least one common terminal bolt.
A shortcoming with respect to the termination of heater coils is that when threaded stud or bolt style termination for heaters is needed, prior art methods require the heating element wire ends to be first secured to heavy and cumbersome terminal bolts; the coil and terminal bolt assembly routed and subsequently secured to the coil support insulators. If the pressure connection method is used so as to allow heating element coils to be first assembled into a heater and then to connect to terminal bolts or threaded studs, this process is cumbersome and labor intensive. Also pressure electrical connections depend too much on the manual skill and attention of the person performing the task unlike a mechanical connection and thus generally are avoided if possible.
When threaded style terminations are required in the industry, there is needed a means to first make secure electrical connections between resistance wire coil ends and lightweight, easy to handle connectors that can later be attached to the terminal bolts or threaded studs whichever is used.
Referring now to FIGS. 2-4, a prior art heater subassembly 20 is disclosed. FIGS. 2 and 3 depict a support plate 21 as part of the subassembly 20. The support plate 21 has a number of openings 23, which are sized to retain insulators 25. The insulators 25 are configured to connect to and support the coils 27 and 29.
The heater assembly 20 is a two stage heater, although more stages could be employed if so desired. The two stage heating is accomplished by the pair of resistance wire coils 27 and 29, with coil 27 representing the first stage and coil 29 representing the second stage.
Coil 27 has opposing terminal ends 31 and 33, with coil 29 having opposing terminal ends 35 and 37. Terminal ends 31 and 35 have a first type of terminal 39 attached thereto. Terminal ends 33 and 37 have a second type of terminal 41 attached thereto. Terminal 41 is a conventional blade end crimp style terminal whereby the end of the resistance wire is crimped to one end of the terminal. The other end is a flat configuration for connection as is well known in the art. Since these blade end crimp type terminals are well known, a further description is not necessary.
Referring now to FIGS. 5 and 7a-7c, the terminal 39 has a crimp end 43 and flat end 45. The crimp end 43 includes a pair of flanges 47, with a slot 49 between the flanges. The slot 49 receives the end of the coil wire and the flanges 47 are crimped to form a tight connection between the coil wire end and crimp end 45. The flat end 45 has an opening 51 that is sized to receive a stud or bolt or other elongated terminal member for connection. As described above, the terminal 39 can hold a bolt during assembly of the heater, with the bolt making the power connection once the heater is finally assembled. In the alternative, the terminal 39 can be used once the heater is completely assembled to attach to a particular stud or bolt using the necessary combination of washers and nuts for a secure connection. Thus, the manufacture of the heater assembly has maximum capability when assembling the heater to accommodate different modes of assembly.
Referring now to FIGS. 2-4 and 6, the arrangement of the coils 27 and 29 produces a termination zone 53 of the coils at one end of the support plate 21. Referring to FIG. 6, one end of a completed heater 60 is shown. The heater 60 includes the support plate 21, insulators 25, and coils 27 and 29, and their respective terminals 39 and 41. The heater 60 includes a circular duct 61 (other shaped ducts could be used) that is linked to the support plate using openings in the duct and the protrusions on the support plate as is well known in the art. The support plate 21 divides the duct into two halves, but other plates could be used to create more sectors of the heater.
The heater 60 supports a power terminal 63, which includes a ceramic bushing 65, with elongated members, e.g., threaded studs 67, extending from each end. One stud 67 attaches to both terminals 39 of the coils 27 and 29 using nut 69 and washer 71 (other combinations of washers and nuts or other fasteners may be employed). The other stud 67 is attached to power. The blade terminals 41 are attached to two other terminals 73 and 74 as conventionally done for these types of heaters. The terminals 73 and 74 have connectors 76 opposite the connection to terminals 41 to complete the circuitry of the heater.
By the configuration of the coils and formation of the termination zone 53, the terminations of the coil ends are located at one end of the heater. By positioning this end into upstream of the flow of air (where ambient air is introduced into the heater), the termination zone is on the cool side of the heater so that the effects of heated air on the terminations is minimized. Also, the terminals are all in the same location, which makes it easier to routing wiring and installing the heater.
The unique configuration of the coils is best seen in FIGS. 2-4 and 6. FIG. 2 represents the coils mounted to the side 75 of the support plate 21 (shown as the right side of the heater of FIG. 6) with FIG. 3 showing the coils mounted to the side 77 of the support plate 21 (shown as the left side of the heater of FIG. 6). For ease of understanding, the sides 75 and 77 each have a reference mark 79.
On side 77, it can be seen that there are two runs of the second stage coil 29 and one run of the first stage coil 27. On the opposite side 75, there is one full run and two half runs of the first stage coil 27, and two half runs of the coil 29. This configuration means that when the first stage heater is used, air passing on both sides 75 and 77 of the support plate is heated. Similarly, during a two stage heating, air passing on both sides is heated from both coils 27 and 29. If the runs on each side were considered to be in thirds, side 77 has two thirds of the coil 29 and one third of the coil 27, with side 75 having two thirds of the coil 27 and one third of the coil 29.
FIG. 4 shows the runs of coils in one drawing, which more clearly depicts the crossovers between the plate 21 and crossovers between coils 27 and 29 on each side of the plate 21. For side 77, coil 29 has both ends 80 of the coil portion (see FIG. 5 to more clearly see the end of the coil portion of the coil) terminate on side 77, with the two runs linked by crossing over at crossover portion 82 to the two half runs on side 75, which are linked by crossover portion 85.
Coil 27 has one coil end 78 terminate on side 77, with one crossover at crossover portion 84 to side 75 to another long run. The long run on side 75 links to one of the short runs on the same side by crossover portion 88, which in turn links to another short run on the same side by another crossover portion 90 so that the coil end terminates on side 75 at end 31 and terminal 39. While the free and uncoiled ends of the coils 27 and 29 could cross over the support plate 21 to attach to the desired terminal as shown in FIG. 6 for coil end 35, the ends of the coils themselves, i.e., 78 and 80, are separated by the support plate 21.
FIGS. 2 and 3 also show the runs of the coils 27 and 29 in a sinusoidal pattern or configuration. Each of the resistance wire coils 27 and 29 has a longitudinal axis generally parallel to an air flow path of the heater. At least a portion of the insulators 25 that support the coils 27 and 29 are offset from the path. These offset insulators 25 when combined with the insulators 25 on the path cause at least a portion of the resistance wire coil to have a sinusoidal shape as disclosed in application Ser. No. 11/987,542 noted above. It is this sinusoidal shape that provides advantages in terms of noise reduction, reduction of the shadowing problem, minimizing vibration resonancy, and better filling the volume of the heater for maximized heat transfer. While this sinusoidal shaped coil configuration is a preferred one, other coil configurations could be employed such as a straight configuration that has no sinusoidal pattern.
While the figures show a particular arrangement of terminals for each side of the plate 21, the terminals 39 and 41 could be switched if the terminations on the heater duct dictated such a switch.
It should be also understood that the configuration of the coils and creation of the termination zone 53 can be used with any types of terminals for the ends 31, 33, 35, and 37 of the coils. Also, while a two stage heater is shown, additional coils could be employed without departing from the equal partitioning of the coils for each stage on each side of the plate and maintaining termination at the cool or upstream end of the heater. The support plate 21 is typically metal in these types of heaters, but it can be any material capable of providing the desired strength and stability during the heater operation, a non-metallic material, composite and the like. The other heat components can also be made of any materials that are capable of functioning in the environment of open coil resistance heaters.
In use, the heater can be used to heat air passing over the coils in the known fashion. Also, the inventive terminal configuration allows the terminals 39 to be attached to one end of the coil prior to heater assembly or during an early stage of the assembly. The lightweight nature of the terminal avoids the problem encountered when heavy bolts have been used in the past. The use of the terminal 39 enables a secure termination at the power terminal to be easily made using nuts and washers.
While the prior art heaters provide adequate means to heat air or a fluid for a heating application, the heaters still are in need of improvement and the present invention responds to this need.